PolarSSL: Implement public key pinning

docs/curl.1

@@ -589,9 +589,16 @@ indicating its identity. A public key is extracted from this certificate and
 if it does not exactly match the public key provided to this option, curl will
 abort the connection before sending or receiving any data.
 
-Added in 7.39.0 for OpenSSL, GnuTLS and GSKit. Added in 7.43.0 for NSS and
-wolfSSL/CyaSSL. sha256 support added in 7.44.0 for OpenSSL,
-GnuTLS, NSS and wolfSSL/CyaSSL. Other SSL backends not supported.
+PEM/DER support:
+  7.39.0: OpenSSL, GnuTLS and GSKit
+  7.43.0: NSS and wolfSSL/CyaSSL
+  7.47.0: mbedtls
+  7.49.0: PolarSSL
+sha256 support:
+  7.44.0: OpenSSL, GnuTLS, NSS and wolfSSL/CyaSSL.
+  7.47.0: mbedtls
+  7.49.0: PolarSSL
+Other SSL backends not supported.
 
 If this option is used several times, the last one will be used.
 .IP "--cert-status"

docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.3

@@ -90,10 +90,16 @@ footer:
 -----END PUBLIC KEY-----
 .fi
 .SH AVAILABILITY
-Added in 7.39.0 for OpenSSL, GnuTLS and GSKit. Added in 7.43.0 for
-NSS and wolfSSL/CyaSSL. Added for mbedtls in 7.47.0, sha256 support
-added in 7.44.0 for OpenSSL, GnuTLS, NSS and wolfSSL/CyaSSL. Other
-SSL backends not supported.
+PEM/DER support:
+  7.39.0: OpenSSL, GnuTLS and GSKit
+  7.43.0: NSS and wolfSSL/CyaSSL
+  7.47.0: mbedtls
+  7.49.0: PolarSSL
+sha256 support:
+  7.44.0: OpenSSL, GnuTLS, NSS and wolfSSL/CyaSSL.
+  7.47.0: mbedtls
+  7.49.0: PolarSSL
+Other SSL backends not supported.
 .SH RETURN VALUE
 Returns CURLE_OK if TLS enabled, CURLE_UNKNOWN_OPTION if not, or
 CURLE_OUT_OF_MEMORY if there was insufficient heap space.

lib/vtls/polarssl.c

@@ -36,6 +36,7 @@
 #include <polarssl/certs.h>
 #include <polarssl/x509.h>
 #include <polarssl/version.h>
+#include <polarssl/sha256.h>
 
 #if POLARSSL_VERSION_NUMBER < 0x01030000
 #error too old PolarSSL
@@ -60,6 +61,15 @@
 /* The last #include file should be: */
 #include "memdebug.h"
 
+/* See https://tls.mbed.org/discussions/generic/
+   howto-determine-exact-buffer-len-for-mbedtls_pk_write_pubkey_der
+*/
+#define RSA_PUB_DER_MAX_BYTES   (38 + 2 * POLARSSL_MPI_MAX_SIZE)
+#define ECP_PUB_DER_MAX_BYTES   (30 + 2 * POLARSSL_ECP_MAX_BYTES)
+
+#define PUB_DER_MAX_BYTES   (RSA_PUB_DER_MAX_BYTES > ECP_PUB_DER_MAX_BYTES ? \
+                             RSA_PUB_DER_MAX_BYTES : ECP_PUB_DER_MAX_BYTES)
+
 /* apply threading? */
 #if defined(USE_THREADS_POSIX) || defined(USE_THREADS_WIN32)
 #define THREADING_SUPPORT
@@ -453,6 +463,61 @@ polarssl_connect_step2(struct connectdata *conn,
       infof(data, "Dumping cert info:\n%s\n", buffer);
   }
 
+  /* adapted from mbedtls.c */
+  if(data->set.str[STRING_SSL_PINNEDPUBLICKEY]) {
+    int size;
+    CURLcode result;
+    x509_crt *p;
+    unsigned char pubkey[PUB_DER_MAX_BYTES];
+    const x509_crt *peercert;
+
+    peercert = ssl_get_peer_cert(&connssl->ssl);
+
+    if(!peercert || !peercert->raw.p || !peercert->raw.len) {
+      failf(data, "Failed due to missing peer certificate");
+      return CURLE_SSL_PINNEDPUBKEYNOTMATCH;
+    }
+
+    p = calloc(1, sizeof(*p));
+
+    if(!p)
+      return CURLE_OUT_OF_MEMORY;
+
+    x509_crt_init(p);
+
+    /* Make a copy of our const peercert because pk_write_pubkey_der
+       needs a non-const key, for now.
+       https://github.com/ARMmbed/mbedtls/issues/396 */
+    if(x509_crt_parse_der(p, peercert->raw.p, peercert->raw.len)) {
+      failf(data, "Failed copying peer certificate");
+      x509_crt_free(p);
+      free(p);
+      return CURLE_SSL_PINNEDPUBKEYNOTMATCH;
+    }
+
+    size = pk_write_pubkey_der(&p->pk, pubkey, PUB_DER_MAX_BYTES);
+
+    if(size <= 0) {
+      failf(data, "Failed copying public key from peer certificate");
+      x509_crt_free(p);
+      free(p);
+      return CURLE_SSL_PINNEDPUBKEYNOTMATCH;
+    }
+
+    /* pk_write_pubkey_der writes data at the end of the buffer. */
+    result = Curl_pin_peer_pubkey(data,
+                                  data->set.str[STRING_SSL_PINNEDPUBLICKEY],
+                                  &pubkey[PUB_DER_MAX_BYTES - size], size);
+    if(result) {
+      x509_crt_free(p);
+      free(p);
+      return result;
+    }
+
+    x509_crt_free(p);
+    free(p);
+  }
+
 #ifdef HAS_ALPN
   if(data->set.ssl_enable_alpn) {
     const char *next_protocol = ssl_get_alpn_protocol(&connssl->ssl);

lib/vtls/polarssl.h

@@ -26,6 +26,8 @@
 
 #ifdef USE_POLARSSL
 
+#include <polarssl/sha256.h>
+
 /* Called on first use PolarSSL, setup threading if supported */
 int  Curl_polarssl_init(void);
 void Curl_polarssl_cleanup(void);
@@ -65,6 +67,7 @@ int Curl_polarssl_shutdown(struct connectdata *conn, int sockindex);
 #define curlssl_version Curl_polarssl_version
 #define curlssl_check_cxn(x) ((void)x, -1)
 #define curlssl_data_pending(x,y) ((void)x, (void)y, 0)
+#define curlssl_sha256sum(a,b,c,d) sha256(a,b,c,0)
 
 /* This might cause libcurl to use a weeker random!
    TODO: implement proper use of Polarssl's CTR-DRBG or HMAC-DRBG and use that

tests/runtests.pl

@@ -2358,6 +2358,7 @@ sub checksystem {
            }
            elsif ($libcurl =~ /polarssl/i) {
                $has_polarssl=1;
+               $has_sslpinning=1;
                $ssllib="polarssl";
            }
            elsif ($libcurl =~ /axtls/i) {